eBay Money Back Guarantee is 30 days, never was 90 days. Before eBay Money Back Guarantee, it was 45 days after payment date. Again no 90 days. Completed listings are kept on ebay for 90 days.
Current time to file a claim on ebay is 30 days after the latest delivery estimate date or 45 days if no date available.
No idea where you got 90 days from.
PayPal Buyer Protect is 180 days for INR and SNAD claims.
My understanding of the time periods and dates and such. Someone correct me if I am wrong.